Methods of inhibiting corrosion using halo-benzotriazoles

ABSTRACT

The use of halo-benzotriazoles as corrosion inhibitors in aqueous systems is disclosed. Halo-benzotriazoles such as chloro-tolyltriazole and bromo-tolyltriazole were found to be more effective corrosion inhibitors than tolyltriazole in the presence of chlorine.

This is a divisional of application Ser. No. 08/778,705 filed Jan. 31997 now U.S. Pat. No. 5,772,919, which is a continuation-in-part ofapplication Ser. No. 08/407,173, filed Mar. 21, 1995 now abandoned.

FIELD OF THE INVENTION

The present invention relates to the control of corrosion in aqueoussystems. More particularly, the present invention relates to theinhibition of corrosion of steel and copper alloys in aqueous systemsthrough application of halo-benzotriazoles to the aqueous system.

BACKGROUND OF THE INVENTION

The use of triazoles for inhibiting the corrosion of copper and ironalloys in a wide variety of aqueous and non-aqueous systems is wellknown. In industrial cooling water systems, benzotriazole andtolyltriazole are used most often. Tolyltriazole is generally preferredbecause of its lower cost. Triazoles are film forming materials thatprovide efficient coverage of metal or metal oxide surfaces in a systemthereby providing protection against corrosive elements present in anaqueous system. In addition to the film forming tendency of variousazoles, they also precipitate soluble, divalent copper ions. Theprecipitation prevents transport of copper ions to ferrous surfaces,where galvanic reactions between copper ions and iron atoms leads topitting corrosion of the ferrous metal.

While the use of azoles for corrosion inhibition is widespread, thereare drawbacks to their use, specifically with tolyltriazole. The mostimportant drawbacks are experienced when azoles are used in combinationwith oxidizing halogens. Oxidizing halogens such as elemental chlorine,bromine, their hypohalous acids, or their alkaline solutions (i.e.,solutions of hypochlorite or hypobromite ion) are the most commonmaterials used to control microbiological growth in cooling watersystems. When copper or iron alloys that have previously been protectedwith azoles are exposed to an oxidizing halogen, corrosion protectionbreaks down. After breakdown, it is difficult to form new protectivefilms in tolyltriazole treated cooling systems that are beingchlorinated, particularly continuously chlorinated. Very high dosages oftolyltriazole are frequently applied in an attempt to improveperformance, often with limited success.

The degradation of protection of azole films in the presence ofoxidizing halogens is well-documented in the literature. For example, R.Holm, et al., concluded that hypochlorite penetrates an intact triazolefilm, leading to higher corrosion rates, and that secondly, hypochloriteattacks the prefilmed triazole surface, disrupting or degrading the film(53rd Annual Meeting of the International Water Conference, Paper No.IWC-92-40, 1992). Lu, et al., also studied interactions of triazolefilms with hypochlorite on copper and copper alloy surfaces ("Effects ofHalogenation on Yellow Metal Corrosion: Inhibition by Triazoles",Corrosion, 50, 422 (1994)). Lu, et al., concluded:

(a) prefilmed tolyltriazole on copper and brass surfaces undergoesdecomposition during chlorination;

(b) the stability of prefilmed tolyltriazole on copper and brass toNaOCl was improved when tolyltriazole was added to the hypochloritesolution;

(c) clean (i.e., non-prefilmed) copper surfaces did not develop goodprotective films when placed in solutions containing mixtures oftolyltriazole and NaOCl.

Thus, the combination of tolyltriazole with NaOCl did not produce acomposition capable of efficient film formation and corrosioninhibition.

The nature of the reaction products when azoles are exposed to oxidizinghalogens in a cooling water system is not clear. The literature teachesthat a compound is formed when chlorine and tolyltriazole are combinedin cooling waters, and that it responds to analytical tests forchlorine. For example, Vanderpool, et al., state that chlorine reactsreversibly with tolyltriazole to produce N-chloro-tolyltriazole. Theyspecifically state, "presumably this compound is not itself aninhibitor." Rather, they teach that it is readily hydrolyzed to theoriginal tolyltriazole and hypochlorous acid so that free tolyltriazolebecomes available for corrosion inhibition ("Improving the CorrosionInhibitor Efficiency of Tolyltriazole in the Presence of Chlorine andBromine", NACE Corrosion/87, Paper No. 157 (1987)). Hollander and Maystated they were able to isolate Ichloro-tolyltriazole from stored, morehighly concentrated solutions, but they also teach that "at lowconcentrations (less than 10 mg/L) rapid hydrolysis made it impossibleto isolate the chloro adducts." Based upon proton NMR analysis, thematerial Hollander and May isolated was chloro-tolyltriazole.

Another observation is that a very characteristic odor is presentwhenever tolyltriazole and chlorine are combined in cooling waters.

In contrast, the present authors have shown that chloro-tolyltriazoledoes not respond to analytical tests for chlorine, despite extendedboiling. And solutions of chloro-tolyltriazole, surprisingly, do notproduce the characteristic odor. Thus chloro-tolyltriazole is clearlydifferent from the tolyltriazole-chlorine reaction product that forms in-situ in cooling water systems.

There are also references in the literature to 5-chlorobenzotriazole(i.e., CAS number 94-97-3!). In "The Water Drop", Volume I No. 2, 1985,Puckorius & Associates state that chlorinated tolyltriazole is effectiveas a corrosion inhibitor and cite R. P. Carr as a reference. Aliterature review of published work by Carr indicates that he actuallyteaches that reactions between tolyltriazole and chlorine do not occurunder cooling water conditions ("The Performance of Tolyltriazole in thePresence of Sodium Hypochlorite Under Simulated Field Conditions", NACECorrosion/83 Paper No. 283, 1983). In this Corrosion/83 paper, Carr doesdiscuss the inhibiting action of a chloro-azole but it is a reference toearlier literature and specifically to the action of5-chlorobenzotriazole and related aryl substituted azoles in sulfuricacid solutions ("Effects of Substituted Benzotriazole on theElectrochemical Behavior of Copper in H₂ SO₄ ", Wu et al., Corrosion,Volume 37, No. 4, 223 (1981)). Since the 1985 Puckorius reference, therehas been widespread use of tolyltriazole in chlorinated cooling systemswith well established performance difficulties, indicating a continuing,unsolved problem in the art.

Other problems are well-known when tolyltriazole and oxidizing halogensare combined in cooling waters. These include a loss in the extent ofprecipitation of transition metal ions such as copper, thus leading toimproved transport and galvanic corrosion, a change in the response ofthe standard spectrophotometric test for tolyltriazole, leading tounintentional overfeed, and the objectionable odor mentioned above. Thisodor can be sensed even when the cooling water originally contained 1ppm tolyltriazole, or less. Since cooling water often passes overcooling towers, evaporation and drift release the objectionable odor tothe local environment.

The present inventors believe that the odorous material isN-chloro-tolyltriazole, that it forms OCl reversibly with tolyltriazolein dilute solution, and that it is absent in the final product when thereaction is run in concentrated solution, i.e.,tolyltriazole+OCl→N-chloro-tolyltriazole-(intermediate)→chloro-tolyltriazole.The present inventors have found no evidence of reversion ofchloro-tolyltriazole to either the odorous intermediate or totolyltriazole. Nor is there any evidence of reactions betweenhypochlorite and chloro-tolyltriazole in dilute aqueous solutions.

SUMMARY OF THE INVENTION

The present inventors have discovered that halo-benzotriazoles such aschloro-tolyltriazole and bromo-tolyltriazole are more effective thantolyltriazole in inhibiting corrosion in aqueous systems. Thehalo-benzotriazoles are substantially more effective than tolyltriazolein the presence of chlorine. Furthermore, when chloro-tolyltriazole isexposed to chlorine, an objectionable odor does not form and thequantity of chlorine that is required to produce a residual in theaqueous system is reduced.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present inventors have discovered that halo-benzotriazoles such aschloro-tolyltriazole and bromo-tolyltriazole are more effective thantolyltriazole in inhibiting corrosion in aqueous systems. Thehalo-benzotriazoles are substantially more effective corrosioninhibitors than tolyltriazole in the presence of chlorine. The efficacyof the present invention is surprising given the prior knowledge thatchlorination of an azole treated system leads to degradation ofcorrosion inhibition performance. Furthermore, the halo-benzotriazolesof the present invention are not subject to the formation ofobjectionable odors when exposed to chlorine as is tolyltriazole, thequantity of chlorine that is required to produce a residual in theaqueous system is notably reduced in comparison to systems treated withtolyltriazole, and the treatment is effective in the presence of sulfideions.

It was discovered that the ex situ preparation of a halo-benzotriazoleprovided a corrosion inhibitor which exhibited a surprising andunexpected activity when compared to a treatment comprising a mixture ofa benzotriazole and a halogen. The results of the studies of the presentinvention clearly show that mere mixtures of a benzotriazole and ahalogen in a cooling water system do not provide the corrosioninhibiting effect of the addition of a halo-benzotriazole prepared exsitu. As further evidence of the surprising activity of an ex situprepared halo-benzotriazole, the present inventors found that thechlorine demand of a system treated in accordance with the presentinvention was significantly reduced. Furthermore, in systems treated inaccordance with the present invention the objectionable odor common tosystems treated with a triazole and halogen was absent.

The halo-benzotriazoles of the present invention can include chloro-,fluoro-, bromo- and iodo- as well as haloalkyl (trifluoromethyl)benzotriazoles. Preferred are chloro-tolyltriazole andbromo-tolyltriazole. The azole may include tolyltriazole, benzotriazole,butylbenzotriazole, mercaptobenzothiazole and the like. The preferredazole is tolyltriazole.

The preferred benzotriazole, tolyltriazole, is such that the preferredhalo-benzotriazole is chloro-tolyltriazole or bromo-olyltriazole. Thepreparation of the preferred chloro-tolyltriazole can be by any suitablemeans. Examples of preparation methods include but are not limited toreactions with hypochlorite, N-chlorosuccinimide, and other chlorinatingagents. A method of forming chloro-tolyltriazole is through the reactionof tolyltriazole with hypochlorite, in which case the final reactionmixture is an alkaline solution that can be used with or without furthermodification. Alternatively, chloro-tolyltriazole can be formed throughthe reaction of tolyltriazole with hypochlorite in acetic acidsolutions, (i.e., hypochlorous acid) and then isolated as a solid. Forconvenience of application, the solid can be redissolved in alcoholssuch as methanol or 2-propanol, aqueous solutions of alcohols or strongalkaline solutions such as sodium hydroxide or potassium hydroxide.

The preparation of bromo-tolyltriazole can be by any suitable means.Examples of preparation methods include but are not limited to reactionswith hypobromite, bromine, and other brominating agents. A method offorming bromo-tolyltriazole is through the reaction of tolyltriazolewith bromine in an aqueous solution and then isolating it as a solid.For convenience of application, the solid can be dissolved in a strongalkaline solution such as sodium hydroxide or potassium hydroxide.

In treating an aqueous system in accordance with the present invention,the chloro-tolyltriazole (hereinafter Cl--TTA) is preferably fedcontinuously to the water. A preferred treatment concentration rangesfrom about 0.5 to 10 parts per million, most preferably at about 3 partsper million. Continuous feed is not, however, a requirement. Thechloro-tolyltriazole can be fed at a concentration sufficient to form aprotective film and thereafter feed can be discontinued for extendedperiods of time.

The halo-benzotriazole treatment of the present invention can be used incombination with other corrosion and/or deposit inhibiting treatmentsknown in the art including but not limited to phosphates, phosphonates,acrylic homo- and copolymers, chelants, and oximes.

The present invention will now be further described with reference to anumber of specific examples which are to be regarded solely asillustrative and not as restricting the scope of the present invention.

EXAMPLES Example 1

The preparation of the solid samples was as follows:

Tolyltriazole (hereinafter TTA) (30 g, 0.225 mol) was dissolved inaqueous acetic acid (60 mL, 1:1 ratio) by heating to 32° C. Sodiumhypochlorite (366 g, 5.25% sodium hypochlorite as a bleach solution) wasadded while maintaining the reaction temperature at ˜20° C. Followingthe addition, the reaction mixture was stirred at room temperature for24 hours. A sticky precipitate formed during this time. The solid wasfiltered and taken into methylene chloride. The solid that did notdissolve was filtered and identified as a mixture of Cl--TTA with minoramounts of TTA and dichloro-tolyltriazole (di-Cl--TTA). The methylenechloride was removed to obtain a yellow solid which was identified as amixture of Cl--TTA with minor amounts of di-CL--TTA. Unless noted, thislatter solid was used in the following Examples.

Example 2

A slurry of TTA (50 g, 0.376 mol) in 25 g of water was warmed to 35° C.Sodium hypochlorite (27.9 g, 0.376 mol, added as 226.8 g of a 12.3%sodium hypochlorite solution) was added over a period of 2 hours. Afterthe addition, the reaction was kept at 45° C. for one hour. During theaddition the pH of the reaction mixture increased to 12 and the solidsdissolved. The final product was analyzed by ¹ H and ¹³ C NMR and LCUVand found to be composed of 81.9% Cl--TTA, 8.8% residual TTA, and 9.3%di-Cl--TTA based on the relative areas in the UV spectra.

On dilution to 1 to 100 ppm azole, with or without pH adjustment toabout 7.2, there was no odor from the halo-benzotriazole solution of thepresent invention.

Example 3

In the schemes below, TTA was present at 100 ppm, in contrast to Example2 where the initial slurry contained about 200,000 ppm. "x" denotes astoichiometric ratio. ##STR1##

Example 4

Cl--TTA, prepared as a solid according to Example 1, was dissolved inmethanol and charged to a simulated cooling water solution. The solutioncontained 319 ppm Ca (calculated as CaCO₃), 7 ppm Mg (calculated asCaCO₃), 190 ppm NaHCO₃, 882 ppm Na₂ SO₄, 1184 ppm NaCl, 5 ppm Cl--TTA,and 2.4 ppm of hydroxyethylidene diphosphonic acid (HEDP). Hypochloritewas absent. The solution was maintained at 120° F. by an admiralty brassheater tube and at pH=7.2 to 7.5 by a pH controller equipped to feedsulfuric acid on demand. The solution was recirculated past the heaterand past both admiralty and copper/nickel alloy corrosion rate meters(CRM). After 1 hour the solution was drained and replaced by anidentical solution with no Cl--TTA. This solution was fed to overflowwhich replenished the system with fresh solution at a rate of about 4%by volume per hour. This system was maintained under these conditionscontinuously until the bright admiralty tube was tarnished, at whichpoint the experiment was terminated. Comparisons were made to identicalexperiments with TTA and benzotriazole.

                  TABLE I    ______________________________________    Admiralty Tube Appearance    Pretreatment 40 hours   94 hours   336 hours    ______________________________________    Cl-TTA       Bright     Bright     Tarnished    TTA          Bright     Tarnished  *    Benzotriazole                 Tarnished  *          *    ______________________________________

                  TABLE II    ______________________________________             Admiralty       Cu/Ni             Corrosion Rate (mpy)                             Corrosion Rate (mpy)    Pretreatment             40 hrs. 94 hrs. 336 hrs.                                   40 hrs.                                         94 hrs.                                               336 hrs.    ______________________________________    Cl-TTA   0.2     0.3     0.5   0.7   0.4   0.8    TTA      <0.1    2.2     *     N/A   5.2   *    Benzotriazole             1.3     *       *     2.0   *     *    ______________________________________     *Experiment previously terminated.

Example 5

Corrosion tests were carried out in the apparatus described in Example 4with water containing 500 ppm Ca, 250 ppm Mg, 25 ppm Malk, 15 ppmo--PO₄, 3 ppm tetrapotassium pyrophosphate, 10 ppm of a 3:1, lowmolecular weight, acrylic acid/allyl 2-hydroxypropyl sulfonate ethercopolymer, 2.4 ppm HEDP, a 3 ppm of either Cl--TTA or TTA. The pH wasmaintained at 7.2 with a blended mixture of air and carbon dioxide at120° F. for 18 hours. Electrochemical corrosion rates were measuredusing admiralty brass (ADM) and low carbon steel (LCS) workingelectrodes. All tests also had both admiralty and LCS coupons in contactwith the solution. The method differed from Example 4 in that the azolewas fed continuously at 3 ppm during these experiments. The azole wassupplied by dissolving the solid in potassium hydroxide solution andthen diluting it into the feedwater for the system. Each experiment wasduplicated: once with an admiralty brass heated tube, and once with alow carbon steel heated tube. Corrosion rates were measured as inExample 4 from admiralty and LCS working electrodes, and by weightchanges of admiralty and LCS coupons. Rates for the coupons weremeasured for the initial day of each run, and a "differential" rate wascalculated for the remaining days of the run by offsetting the initialrate from the overall rate.

                  TABLE III    ______________________________________    CRM Corrosion Rates: Values at end of six days (mpy)              LCS Heated Surface ADM Heated Surface              Cl-TTA  TTA        Cl-TTA                                       TTA    ______________________________________    LCS       0.2     0.4        0.45  0.75    ADM       0.00    0.00       0.05  0.07    ______________________________________

                  TABLE IV    ______________________________________    Gravimetric Coupon Corrosion Rates (mpy)    (First day and differential rates)                  LCS              ADM                  Heated Surface   Heated Surface                  Cl-TTA  TTA      Cl-TTA                                         TTA    ______________________________________    Day 1 LCS     4.6     3.0      3.4   2.9    Day 6 LCS (diff.)                  0.25    0.33     0.25  0.25    Day 1 ADM     1.9     2.1      1.6   1.8    Day 6 ADM (diff.)                  0.00    0.20     0.00  0.10    ______________________________________

Example 6

The method of Example 5 was followed, except a solution of sodiumhypochlorite was added after 20 hours and continued for an additional 72hours. The feed rate of the sodium hypochlorite was controlled toproduce a "chlorine residual" of about 0.1 to 0.3 ppm as Cl₂ using astandard DPD spectrophotometric test on the recirculating water. For theexperiment with Cl--TTA, the feed rate of the sodium hypochlorite wasabout 30% of that required for TTA. For TTA, the characteristic odor wasdetected immediately after the first hypochlorite was added. WithCl--TTA, there as no odor upon initiating hypochlorite addition, andonly a trace was sensed just prior to concluding the four day run.

                  TABLE V    ______________________________________    CRM Corrosion Rates: Values at 90 hour mark (mpy)                    LCS Heated Surface                    Cl-TTA  TTA    ______________________________________    LCS             0.5     2.3    ADM             0.06    0.02    ______________________________________

                  TABLE VI    ______________________________________    Gravimetric Corrosion Rates (mpy)                      LCS Heated Surface                      Cl-TTA  TTA    ______________________________________    Day 2 to 4 LCS    1.1     2.6    Day 4 LCS (diff.) 0.4     1.4    Day 2 to 4 ADM    1.1     1.2    Day 4 ADM (diff.) 0.15    0.85    ______________________________________

Example 7

Solutions of azole at 6 ppm were made in deionized water, and the pH wasadjusted to 7.0. Cu⁺² ion was added (0.1 ppm from cupric sulfate) andthe pH was again adjusted to 7.0. A sample was digested with nitricacid, analyzed for copper, and a second sample was filtered (0.2 micronpore size), digested, and analyzed for copper. The ratio was expressedas "% soluble Cu":

                  TABLE VII    ______________________________________    Sample         % Soluble Cu    ______________________________________    TTA            15    TTA + NaOCl    90    Cl-TTA         13    ______________________________________

Example 8

Admiralty brass corrosion coupons and working electrodes were coatedwith a sulfide layer by exposing the metal to a sodium sulfide solutionfor 18 hours. These samples were rinsed and dried. Corrosion tests werecarried out in aqueous solutions in stirred beakers containing 500 ppmCa, 250 ppm Mg, 25 ppm Malk, 15 ppm o--PO₄, 3 ppm tetrapotassiumpyrophosphate, 10 ppm of a 3:1, low molecular weight, acrylic acid/allyl2-hydroxypropyl sulfonate ether copolymer, 2.4 ppm HEDP, and the pH wasmaintained at 7.2 with a blended mixture of air and carbon dioxide at120° F. for 18 hours. Electrochemical corrosion rates were measuredusing admiralty brass or low carbon steel working electrodes. All testsalso had both admiralty and LCS coupons in contact with the solution.

Each solution was tested with and without addition of sodiumhypochlorite (added after 1 hour exposure). In a separate, but otherwiseidentical experiment, clean low carbon steel working electrodes wereused in place of the sulfide-exposed admiralty brass, but thesulfide-exposed brass coupons were present as a source of copper. At theconclusion of the experiment, a sample of the supernatant solution wastaken and analyzed for copper. Analyses were taken with and withoutfiltration through a 0.2 micron membrane filter.

                  TABLE VIII    ______________________________________                    Admiralty Low Carbon                    Brass     Steel            NaOCl   Corrosion Corrosion                                      Copper (ppm)    Azole   (ppm)   Rate (mpy)                              Rate (mpy)                                      Unfiltered                                             Filtered    ______________________________________    none    0       1.01      5.4     0.354  0.103    3 ppm TTA            0       0.07      1.2     0.014  0.014    3 ppm   0       0.06, 0.05                              1.0     0.005  0.004    Cl-TTA    none    2.0     2.09      5.2     0.417  0.059    3 ppm TTA            2.0     0.45      2.6     0.133  0.066    3 ppm   2.0     0.13      1.7     0.086  0.039    Cl-TTA    ______________________________________

Example 9

A synthetic sea water was formulated from deionized water plus 1010 ppmCa as CaCO₃, 5226 ppm Mg (as CaCO₃), 18971 ppm Cl, 2660 ppm SO₄, 117 ppmM-alkalinity (as CaCO₃), 5 ppm azole (see below), and the pH wasmaintained at 7.8 with a blended mixture of air and carbon dioxide at100° F.

Admiralty brass electrodes were exposed to this medium for 1 hour andthen they were transferred to identical water with no azole present.Electrochemical corrosion rates were measured for 18 hours.

                  TABLE IX    ______________________________________                    Mean Electrochemical    Azole           Corrosion Rate (mpy)    ______________________________________    Benzotriazole   40    5-Butylbenzotriazole                    15    Tolyltriazole   6    Chloro-tolyltriazole                    3.2    ______________________________________

Example 10

Sodium hypochlorite (12.2%, 204.9 g, 0.336 mol) was added over 90minutes to a stirring slurry of benzotriazole (40 g, 0.336 mol) in 30 gof water at room temperature. Following the addition, the reactionmixture was held at 45°-50° C. for one hour. Upon cooling, a precipitateformed. A clear yellow solution was obtained after adjusting the pH to11. The final product was analyzed by LC/MS and ¹³ C and ¹ H NMR andfound to be composed of 54.6% chloro-benzotriazole (Cl--BZT), 23.9%residual benzotriazole, and 21.5% di-chloro-benzotriazole (di-Cl--BZT).

Example 11

Bromine (12.5 g, 0.078 mol) was added to a stirring slurry of TTA (10 g,0.075 mol) in 66 g of water in a reactor protected from light, whilemaintaining the temperature at <25° C. After the addition, the reactionmixture was held at 35°-40° C. for one hour. Upon cooling, adjusting thepH to 11-12 did not produce a clear solution. The small amount ofprecipitate that formed upon standing was removed by filtration, the pHof the filtrate was adjusted to neutral, and the resulting precipitatefiltered. This solid was characterized by LC/MS and ¹³ C and ¹ H NMR andfound to be composed of 90.5% bromo-tolyltriazole (Br--TTA), 4.9%residual TTA, and 4.2% di-bromo-TTA.

Example 12

The method of Example 8 was followed, using samples from Examples 2, 11and 12 at 1 to 4 ppm total actives. The following were the 18 houraveraged electrochemical corrosion rates:

                  TABLE X    ______________________________________                                      Average            Conc                      Corrosion    Azole   (ppm)      Source   NaOCl Rate (mpy)    ______________________________________    Cl-BZT  1          Ex. 11   none  0.21            2                         0.09            4                         0.03    Cl-BZT  1          Ex. 11   2 ppm 0.55            2                         0.25            4                         0.09    Cl-TTA  1          Ex. 2    none  0.14            2                         0.09            4                         0.08    Cl-TTA  1          Ex. 2    2 ppm 0.58            2                         0.24            4                         0.09    Br-TTA  1          Ex. 12   none  0.17            2                         0.11            4                         0.07    Br-TTA  1          Ex. 12   2 ppm 0.45            2                         0.16            4                         0.09    TTA     1                   none  0.13            2                         0.14            4                         (n/a)    TTA     1                   2 ppm (n/a)            2                         0.45            4                         0.27    ______________________________________

The above examples show that the halo-benzotriazoles of the presentinvention are effective corrosion inhibitors even in the presence ofchlorine.

While the present invention has been described with respect toparticular embodiments thereof, it is apparent that numerous other formsand modifications of this invention will be obvious to those skilled inthe art. The appended claims and this invention generally should beconstrued to cover all such obvious forms and modifications which arewithin the true spirit and scope of the present invention.

What is claimed is:
 1. A method of reducing chlorine demand in anaqueous system being treated with chlorine to inhibit microbiologicalgrowth comprising adding to said aqueous system being treated withchlorine an amount effective to reduce the chlorine demand of ahalo-benzotriazole prepared ex-situ said aqueous system.
 2. A method ofeliminating the objectionable odor which is present when chloride isadded to an aqueous cooling water system which is treated with an azolefor corrosion control comprising adding to said aqueous cooling watersystem an amount effective to eliminate the objectionable odor of ahalo-benzotriazole formed ex-situ said aqueous cooling water system bythe reaction of tolyltriazole and hypochlorite.
 3. The method of claim 1wherein said halo-benzotriazole is selected from the group consisting ofchloro-tolytriazole and bromo-tolyltriazole.
 4. The method of claim 1wherein said halo-benzotriazole is added to said aqueous system at aconcentration of greater than about 0.5 parts per million.
 5. The methodof claim 1 wherein said halo-benzotriazole is added to said aqueoussystem at a concentration of from about 0.5 parts per million to about10 parts per million.
 6. The method of claim 1 wherein saidhalo-benzotriazole is selected from the group consisting ofmono-halo-benzotriazole and a mixture of mono-halo-benzotriazole anddi-halo-benzotriazole..
 7. The method of claim 2 wherein saidhalo-benzotriazole is selected from the group consisting ofmono-halo-benzotriazole, and a mixture of mono-halo-benzotriazole anddi-halo-benzotriazole.